Query on pciE lane usage

forteh

forteh

forteh

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Hi all, having a real brainfart with my pciE lanes and slots and hoping you can clear up my stupidity!

I have a 5800x3D on an msi B450M mortar max with a 3080ti and an intel 750 pciE nvme drive as the primary boot drive (with 3xSATA drives for storage)

Specs are below: -
Screenshot_20221114-072236.png


My query is, am I forcing the GPU slot to run at pciE 3x8 because I have the intel SSD in the pciE 2x16 slot?

My intention is to get an M2 drive at some point in the near future but I want to know if I should be looking to ditch the intel drive if it's likely to be slowing the GPU down. From what I've read the ryzen has 20 pciE lanes, the GPU uses 16 and the NVME uses 4 so if I were to add an M2 drive in addition to the intel would it then cripple the system elsewhere?
 
Thanks, that's pretty much as I suspected (not that I'm getting bad performance from the 3080ti), the intel drive is a hangover from my old 2500k system and is slower than most pciE3 nvme drives so its days were likely numbered anyways.
I presume the M2 slot next to the GPU is the preferred one to use?

I primarily use the machine for DCS vr so the most throughput I can get the better!
 
The intel is 400gb so ideally no smaller than that, I would probably go for 1tb though - hoping for something coming up in the sales soon :)

edit: I'm guessing that one M2 slot uses CPU lanes and the other M2 slot uses chipset lanes? Would I be better to utilise the chipset ones over the CPU ones, the manual states that if I put an M2 in slot2 then it disables one of the pciEx1 slots. Would using the chipset lanes then take away bandwidth from the USB etc?
 
Last edited:
alec said:
from https://www.msi.com/Motherboard/B450M-MORTAR-MAX/Specification
  • 1 x PCIe 2.0 x16 slot (PCI_E4, supports x4 mode)1
(1) PCI_E4 slot will be unavailable when an M.2 SSD is installed in the M2_2 slot

There is no interaction with main x16 slot.

Does GPUZ show your graphics card run in x8 mode?
Click to expand...

Perhaps this is partly the cause of my confusion, I'm not sure exactly which slots are using which lanes and which are sharing and which are not!
Stupidly I haven't checked the simple stuff like gpuz:rolleyes: Will do so after work :)
 
mickyflinn said:
Looked at this again because the motherboard supports crossfire I thought using the intel m2 in pcie_E4 would share the pcie3 lanes from the gpu . Crossfire can be supported threw the chipset so therefore It looks like that slot is conected by the chipset .

Sorry for the confusion.
Click to expand...
No issues at all, as I said it's probably my next upgrade :)

Tetras said:
The second full length PCI-E slot has 4 lanes (from chipset) which are shared with the second M.2 slot. If the second M.2 slot is used, then the PCI-E slot doesn't work.

PCI-E slot 2 and 3 (the little ones) also share lanes.
Click to expand...

So I should be able to use the top M2 slot next to the CPU without any detriment to GPU or chipset performance? In turn technically I could run both the top M2 (using CPu lanes) and the intel SSD (using chipset lanes) concurrently, alternatively run a pair of M2 drives if I ditch the intel SSD from slot 4.

I don't have anything that will fit into slots 2 & 3 :D
 
Well the answer is, it's running at pciE 3.0x16 according to gpuZ , really don't know why I didn't check that first!
Either way you guys have been very helpful will helping me understand the pciE lanes and how they interact with one another, now to wait for a decent sale on an M2 :)
 
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